Method of manufacturing release sheet

ABSTRACT

The present invention provides a release agent formed by reacting an organopolysiloxane compound having at least one hydrogen atom with a hydrocarbon compound having at least one double bond which reacts with said hydrogen atom and a manufacturing method thereof. The release agent of this invention, which makes substantially no migration into any pressure sensitive adhesive layer, is well adaptable to whichever process, extrusion laminating process or coating process.

This application is a continuation of application Ser. No. 07/641,633,filed Jan. 17, 1991, now U.S. Pat. No. 5,213,743, which in turn is acontinuation of application Ser. No. 07/300,684, filed Jan. 19, 1989 andnow abandoned, which in turn is a division of application Ser. No.07/065,469, filed Jun. 23, 1987 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel release agent and amanufacturing method of a release paper with use thereof and moreparticularly, pertains to a novel release agent which is substantiallyfree of migration into the layer off any pressure sensitive adhesive anda method of efficiently and economically manufacturing release paperwith use thereof by way of extrusion lamination or coating process.

2. Description of the Prior Art

Heretofore, the manufacturing method of silicone base release paper isprincipally based on a coating process, in which usually, a layer oflaminated polyethylene is featured on a substrate like paper, etc., andfurther, a release layer is coated on the surface thereof. The releaseagent employed in this process consists of polymethyl hydrogen siloxaneand vinyl group containing polydimethyl siloxane, and addition ofplatinum, catalyzer and heat induces their addition reaction, causingcuring and formation of release coating. According to this process,however, it thus needs to be prepared by mixing the ingredients andsubjecting the mixture to the addition reaction. This process involvesnot only problems in insufficient curing, short pot life, etc., butdifficulties in practical uses because of complicated operation andhandling.

On the other hand, the release layer may be formed on the substrate atonce by extrusion lamination process. The resin laminated in this wayitself has a certain releasability. As such releasable resins, ethylene-α-olefin copolymer elastomer, etc., are used and they are preferablefor acrylic pressure sensitive adhesives. In the aforementionedextrusion lamination process, however, there is apprehension regardingheat and solvent resistance, etc., at the time of coating of acrylicpressure sensitive adhesives and scattering of release potential withregard to the acrylic pressure sensitive adhesives and the increaseresistance to release with the lapse of time. Since ethylene-α-olefincopolymer elastomer, when singly used, is difficult to extrude, it isused in mixture with polyethylene. The smaller the mixing proportion ofsaid elastomer, the more releasing effect will be lost; but conversely,with its increasing proportions, said elastomer's property will becomestronger, and the film strength lower; moreover, such problems inprocessing as blocking. etc., will be induced.

And in Patent Publication No. Sho 60-5628, a releasable laminate filmformed by laminating on a substrate a thermoplastic resin prepared withaddition of non-cure type organopolysiloxane is proposed. But such areleasable laminate film shows high resistance to release and producesbleeding to the surface of silicone even at room temperature; therefore,it can not necessarily be said adequate for pressure sensitive adhesivetapes or sheets.

The present inventors, in an effort to overcome such problemshereabove-mentioned, developed a manufacturing method of a release agentwhich comprises extruding a mixture of a silicone base release agent andpolyolefin and, then, getting said release agent bled to the surface bysubjecting it to a heat-treatment, followed by fixing by curing, andearlier, they filed an application for the patent on this method (U.S.Ser. No. 885,854 ) now U.S. Pat. No. 4,702,874. Said method, however, isdisadvantageous in that it requires a curing treatment by treatment withsuch a catalyzer as chloroplatinic acid, etc.

SUMMARY OF THE INVENTION

This invention has been intended to solve the problems of prior art ashereabove-mentioned. Its object is to provide a release agent whichmakes substantially no migration into the pressure sensitive adhesivelayer and which is suitable for whichever process, extrusion laminationprocess or coating process.

Other objects and advantages of this invention will become clearer fromthe following, detailed description.

DETAILED DESCRIPTION OF THE INVENTION

Thus a first aspect of this invention resides in a release agent formedby reacting an organopolysiloxane compound having at least one hydrogenatom with a hydrocarbon compound having at least one double bond whichreacts with said hydrogen atom; a second aspect of this invention, amanufacturing method of a release paper characterized in that on asubstrate of paper, cloth, film, etc., there is extruded a mixture of apolyolefin and a release agent produced by reacting anorganopolysiloxane compound having at least one hydrogen atom with ahydrocarbon compound having at least one double bond which reacts withsaid hydrogen atom, thereby forming a laminate, and that the releaseagent contained in the mixture layer of the aforementioned laminate islocalized by letting it bleed to the surface of said mixture layer; anda third aspect of this invention, that on a polyolefin film of asubstrate having such a film, there is coated a solution havingdissolved therein a release agent formed by reacting anorganopolysiloxane compound having at least one hydrogen atom with ahydrocarbon compound having at least one double bond which reacts withsaid hydrogen atom.

Thus the release agent of this invention may be obtained by reacting anorganopolysiloxane compound having at least one hydrogen atom with acarbon compound having at least one double bond which reacts with saidhydrogen atom.

As the organopolysiloxane compounds having at least one hydrogen atom,there may be mentioned polymethyl hydrogen siloxane, polymethylhydro-dimethyl siloxane copolymer, etc.

As the hydrocarbon compounds having, at least one double bond whichreacts with the hydrogen atom of the aforementioned organopolysiloxanecompounds, there may be mentioned α-olefin, polyethylene wax,1,4-polybutadiene, 1,2-polybutadiene, polybutene, 9-octadecene, etc.,and their mixtures.

Illustrating a manufacturing method of the release agent, polymethylhydrogen siloxane (including polymethyl hydro-dimethyl siloxanecopolymer) and α-olefin having a vinyl group at its terminal are mixedand the mixture is subjected to addition reaction by warming, withchloroplatinic acid added as the catalyzer. The reaction productobtained is refined by cleaning several times with acetone, etc.,followed by drying.

In manufacturing a release paper by way of extrusion using the releaseagent synthesized as hereabove-described, although impossible tocomprehensibly specify on account of effect of varying silicon contents,the amount of said release agent to be mixed should be approx. 1-10% byweight in proportion to polyolefin, or more preferably, 2-5% by weight,when its silicon content is 50%. The mixture is kneaded and pelletizedby a pelletizer, to be used as a mixture layer resin (extrusion resin).Master batch operation using a twin-screw extruder is also feasible.This material may be also effectively utilized as a release agent for avariety of pressure sensitive adhesives or hard urethane foam, etc., orfor medicines or as a poultice separator, by adjusting its amount added.

As polyolefin used according to this invention, preferable arepolyethylene, polypropylene, 4-methyl pentene-1 resin and copolymerswith ethylene such as ethylene-propylene copolymer, ethylene-vinylacetate copolymer, ethylene-acrylic acid copolymer, etc., and theirmixtures, etc. Of the polyethylene, linear low density polyethylenehaving densities of 0.910-0.955 g/cm³ are especially excellent in lowspeed range peeling and are advantageous in that they may beheat-treated in a short period of time, because they permit hightemperature heat treatment. Besides, in order to positively promotelocalization of bleeding, tackifiers or polyvinyl ether, etc., fromwhich plasticizer effect for polyolefin may be expected may be added.And by adding calcium carbonate, titanium dioxide, talc, kaolin, powdersilica, zeolite, etc., releasability may be controlled, or pressuresensitive adhesive tapes which permit lap joint may be achieved.Furthermore, through joint use of embossing process, the releasabilitymay be controlled.

The release layer resin obtained in this way is extruded on a substrateby use of an extrusion laminator, thereby forming a release layer on thesubstrate. Substrate forms used according to this invention includepaper, cloth, film, metal foil and their laminates, etc.

When laminated on the substrate, the release agent is bled and localizedto the surface of the mixture layer of the release layer, simultaneouslyas it is extruded, on account of the heat produced at the time ofextrusion lamination. But if the localization is inadequate, thelaminate should be heat-treated. Due to the heat evolved at the time ofextrusion lamination or by the reheat-treatment the release agentcontained in the mixture layer is bled to the surface of the mixturelayer, to be localized; as a result, similar state will be brought aboutas that obtained by coating some release agent on the surface ofpolyethylene layer as in a conventional method.

According to this invention, it is allowed to interpose an adhesionenhancing layer of polyethylene, etc., between the release layer and thesubstrate for improvement in adhesion therebetween.

On the other hand, for manufacturing the release paper by the coatingprocess using the release agent of this invention, the hithertowell-known method is usable. Thus the release agent of this invention isdissolved in such a solvent as toluene, etc., to have its 1-5% solution,and this solution is coated on a polyolefin film, followed by drying.The coating may be subjected to heat treatment, as required. The amountof the agent to be coated may be in the normal range, e.g., the range of1.5 g/m² -0.6 g/m².

The release agent of this invention will provide affinity to non-solventsilicone, particularly when blended into polyolefin laminate layer ofthe non-solvent silicone coating substrate, and on this account, it isfinding preferable applications in curtailment of spots, pinholes, etc.,when it is coated, in improvement in control on the accuracy of thecoating amount and further, in manufacture of high quality releasepapers.

The feature of the present invention is to provide a release agentobtained by reacting an organopolysiloxane compound having at least onehydrogen atom with a hydrocarbon compound having at least one doublebond which reacts with said hydrocarbon atom, i.e., a release agentcomprising a so-called comb-form copolymer obtained by grafting chainsof hydrocarbon compounds onto an organopolysiloxane compound as a mainchain.

In a mixture of the release agent of the comb-form copolymer and apolyolefin, the organopolysiloxane compound main chain is localized andoriented to the surface of the polyolefin, i.e., the air side. This hasalready been confirmed by ATR-IR analytical results. On the other hand,the chains (graft branches) of the hydrocarbons have high compatibilitywith the polyolefin, so that sometimes they produce chemical bonds,thereby exhibiting anchoring effect as if they extend their roots in thepolyolefin. Thus the organopolysiloxane compound main chain is broughtinto a state of being firmly fastened to the surface of the polyolefin,substantially foreclosing its migration into the pressure sensitiveadhesive layer.

In the following, this invention will be described in connection withexamples and comparative examples, but obviously its claim coverage isnot limited to these modes only. In the following, parts and % arerespectively meant to represent values by weight, unless otherwisespecified.

EXAMPLE 1

Into a reactor, 45.6 parts of polymethyl hydrogen siloxane (P=300,MW=22,000 ), 54.4 parts of α-olefin ("DIALEN-30", manufactured byMitsubishi Kasei Koryo (Chemical Industry)) and 8 parts of 0.1% H₂ PtCl₆·6H₂ O tetrahydrofuran solution were charged, to undergo additionreaction at 80° C. for 8 hr and, then, to be further reacted at 130° C.for 18 hr. The reaction was stopped when the viscosity of the reactionproduct reached approx. 10,000 cps. The reaction product was cleanedthrice with acetone, to remove unreacted part, for its refinement,followed by drying. The silicon content of the release agent obtained inthis way was 45.6%.

EXAMPLE 2

Three percent of the release agent obtained in Example 1 in proportionto low density polyethylene ("M-10P", manufactured by Mitsui SekiyuKagaku MI: 9.5, density: 0.917 g/cm³) was added thereto, to preparepellets for mixture layer at a dies temperature of approx. 200° C. byuse of a pelletizer. The low density polyethylene as used for themixture layer was separately prepared as an adhesion enhancing layer.

As the substrate, 73 g/m² of CLUPAK unbleached kraft was used;polyethylene for adhesion enhancing layer was extruded at a diestemperature of 300° C. by use of a conventional co-extrusion laminatorand the pellets for mixture layer was simultaneously extruded at a diestemperature of 260° C., thereby yielding a laminate of a three layerstructure of substrate layer--adhesion enhancing layer--mixture layer.The thickness of the mixture layer obtained was 15 μm, and the thicknessof the adhesion enhancing layer 15 μm.

Then a sheet form was cut from the three layer laminate obtained in thisway and was subjected to a heat treatment at 120° C. for 20 min, withthe release layer surface turned upward.

With the release paper thus obtained, the release potential and theresidual adhesive strength were measured by the undermentioned method.The results are put up in Table 1.

Pressure Sensitive Adhesive Tape

An acrylic pressure sensitive adhesive kraft tape ("ELM TAPE"manufactured by Soken Kako) was prepared to be 25 mm width×210 mmlength, for it to be used in the tests.

Measuring Conditions

The aforementioned pressure sensitive adhesive tape was stuck with theaforementioned release paper by reciprocally applying pressure by anapplication device with a 4.5 kg dead weight at a speed of 5 mm/sec andthe release potential and the residual adhesive strength of the productwere measured under the following conditions:

The measurements were taken after the paper and the tape stuck togetherhad been subjected to ageing by leaving for 20 hr under weight of 20g/cm² applied thereon in an atmosphere of temperature 70° C. andhumidity 65% RH and, then, left cooling.

Measuring Method

The measurements were taken at a peeling angle of 180 degrees, using anautograph tensile tester ("STROGRAPH-R" manufactured by Toys Seiki), forthe low speed range (0.3 m/min ) peeling, and a high speed peelingtester (manufactured by Tester Sangyo), for the high speed range (3m/min and 20 m/min). The condition at the time of measurements were 23°C. and 65% RH.

EXAMPLE 3

In manufacturing the similar laminate as in Example 2, the extrusion wasmade under the same conditions as in Example 2, except that a coolingroll which was coated with tetrafluoroethylene-hexafluoroprorylenecopolymer was used at the time of making extrusion lamination.

The release paper obtained was put to the similar tests as in Example 2.The results are given in Table 1. The localization of the release agentwas adequate. By coating the cooling roll with the foregoing copolymer,the surface of the roll is made non-polar, which accelerates thelocalization of the release agent.

EXAMPLE 4

The release agent obtained in Example 1 was dissolved in toluene to haveits 3% solution, which was heated to 40° C. and coated on a biaxialorientation polypropylene film (OPP) (50 um). Its amount applied was0.7g/m². The release paper thus obtained was put to the similar tests asin Example 2. The results are shown in Table 1.

Comparative Example 1

Use was made of only the low density polyethylene "M-10P" used inExample 2, which was extruded just as in Example 2 and the releasepotential and the residual adhesive strength of the product weremeasured. The results are given in Table 1.

Comparative Example 2

The release paper obtained in Comparative example 1 was subjected to aheat treatment at 120° C. for 20 min and the release potential and theresidual adhesive strength of the treated product were masured. Theresults are listed in Table 1.

Comparative Example 3

A release paper was obtained similarly as in Example 2, except that thelocalization was inadequate and that it was not subjected to the heattreatment, and its release potential and residual adhesive strength weremeasured. The results are presented Table 1.

                                      TABLE 1                                     __________________________________________________________________________                     Peeling rate    Residual adhesive strength (2)                      Localization                                                                            0.3 m/min                                                                           3 m/min                                                                            20 m/min                                                                           (0.3 m/min) (%)                              __________________________________________________________________________    Example 2                                                                            120° C. × 20 min                                                            50    95  110  98.3                                         Example 3                                                                            Made at the time of                                                                      45    90  115  97.8                                                making lamination.                                                     Example 4                                                                            --         50    75   85  92.1                                         Comparative                                                                          --        390   600  520  65.3                                         example 1                                                                     Comparative                                                                          120° C. × 20 min                                                           360   520  470  73.5                                         example 2                                                                     Comparative                                                                          --        170   270  290  75.0                                         example 3                                                                     __________________________________________________________________________     (1) The unit for the measured values is g/25 mm in all cases.                 ##STR1##                                                                 

As hereabove described, the release agent of this invention does notbleed at room temperature and gives excellent release potential andresidual adhesive strength. And when manufacturing a release paper bythe extrusion lamination process, using the release agent of thisinvention, curing treatment is not required and when coating process isused, its mere dissolution in a solvent will do without the need ofpreparation by mixing and making addition reaction, every time coatingis done; accordingly, productivity is greatly elevated.

What is claimed is:
 1. A method of manufacturing a release sheetconsisting of the steps of:extruding a mixture consisting of a) apolyolefin resin and b) a graft polymer onto a substrate to form alaminate, said graft polymer having been formed by reacting anorganopolysiloxane compound having at least one hydrogen atom with ahydrocarbon compound having at least one double bond reactive with thathydrogen atom; and heating the laminate to cause the graft polymercontained in the extruded mixture to bleed onto and become localized atthe surface of the mixture.
 2. A method of manufacturing a release sheetconsisting of the steps of:extruding a mixture consisting of a) apolyolefin resin and b) a graft polymer onto a substrate to form alaminate, said graft polymer having been formed by reacting anorganopolysiloxane compound having at least one hydrogen atom with ahydrocarbon compound having at least one double bond reactive with thathydrogen atom; and causing the graft polymer contained in the extrudedmixture to bleed onto and become localized at the surface of themixture.